How to Kill Crabgrass

Published December 6, 2019
Front lawn with crab grass

You can kill crabgrass with a herbicide or try natural types of weed killers. Since crabgrass isn't a perennial, but reseeds itself, you can also use a crabgrass preventer.

How to Identify Crabgrass and Why You Don't Want It

Most people don't like the look of crabgrass in their yards. Crabgrass is blamed for crowding out more desirable lawn grasses. Crabgrass has a matted clumpy look that contrasts sharply with other lawn grasses.

Broad Leaf Blades

Crabgrass leaf blades are broad and radiate out from the clustered center to create a thick mat with a clump appearance. It's easy to distinguish from other grasses, since the blades are much wider than most lawn grasses. When crabgrass first begins to grow in your yard, the center of the plant grows flat on the surface and spreads out horizontally. As more blades emerge from the center, they will also branch out to grow horizontally.

Identifying Crabgrass

If you have any bare places in your lawn, crabgrass will quickly move in, especially in open sunny areas. Crabgrass is adaptive and can grow vertical blade shoots, often making it difficult to identify if you're not familiar with it. However, one distinct identifier is the line that runs along the center of the blade, often referred to as a fold line.

How to Kill Crabgrass Using Post-Emergent Herbicides

Often referred to as post-emergent herbicides, crabgrass herbicide killers come in sprays or pellets. It is used to kill the crabgrass that's taken root in your lawn. To use the pellets or granules, you'll need to use a broadcast spreader. Some herbicides include a fertilizer formula. You'll want to use a hand-pump garden sprayer to direct the spray onto individual clumps of crabgrass.

Tips for Using Post-Emergent Herbicide for Crabgrass

The most important thing to remember when using any herbicide is to follow the manufacturer's directions. Pay special attention to any warnings since herbicides linger and children and pets can be vulnerable to the harmful chemicals.

  • The type of lawn grass you use will determine how much post-emergent herbicide spray or pellets ois needed to kill the crabgrass.
  • The product label should advise how long to keep pets off the lawn after application.
  • Some products require you to wait one year before allowing grazing animals back onto the turf.
  • Don't spray if it's windy; this will cause chemical drift that could harm ornamental plants and trees.
  • Don't use crabgrass pre-emergent or post-emergent herbicides in flower beds or vegetable beds!
Pest control technician

What Is a Crabgrass Preventer?

A crabgrass preventer, also called a pre-emergent herbicide, is not the same thing as a crabgrass killer. A pre-emergent herbicide prevents crabgrass seeds from germinating.

Pre-Emergent Herbicides Kill Crabgrass Seeds

Herbicide preventers are specifically designed to kill the germinating seeds, so they cannot form and sprout into active weeds in your yard. If crabgrass is growing in your yard, you'll need a weed killer instead of a preventer. You need to check with the product manufacturer on the proper use of any crabgrass preventer. However, some attributes of this type of pre-emergent are found in most of the herbicides available.

Tips for Using a Crabgrass Preventer

A few easy tips can ensure success in using a crabgrass preventer (pre-emergent). Be sure to read the manufacturer's label instructions for additional product use information.

  • Crabgrass preventers are effective on other broadleaf weed seeds beginning to germinate.
  • You cannot use a crabgrass preventer at the same time you sow grass seed. Grass seed can fall victim to a crabgrass preventer. Refer to the product label for instructions on timing of lawn seeding and applying crabgrass preventer.
  • Most fertilizers cannot be used with or immediately after a preventer application.
  • The best time to apply crabgrass pre-emergent (preventer) is when the soil is between 50°F and 55°F since the germination temperature for crabgrass is 62°F.
  • Apply the crabgrass preventer in early spring before crabgrass emerges from the ground.
  • If using a preventer in the spring, you'll need to sow your lawn with grass seeds during mid-summer to ensure both applications are effective.
Smooth crabgrass

Lawn Herbicides Controversial Health Risks

Herbicides are controversial when it comes to health-related issues for those using and living with treated lawns. This is especially of concern when lawns are repeatedly treated with herbicides.

Herbicides Contribute to Runoff Pollution

Another pause for concern when using a herbicide to kill crabgrass is the potential runoff into streams, creeks and storm drains. Urban areas attribute to runoff pollution from the chemicals found in herbicides and lawn fertilizers.

Natural Ways to Kill Crabgrass

There are several ways you can kill crabgrass without the need of herbicides. These methods may require a small amount of labor, but you can relax knowing you've not added any harmful chemicals to your lawn.

Boiling Water

Boiling water always works as a weed killer. The hot water will instantly kill any plant life it touches. You can use a sprayer got better control. You can cover the dying crabgrass with compost or compost/soil combination. Cover the compost completely with grass seed and lightly cover up the seeds. Water enough to moisten the soil. Water regularly until the grass comes up. This method ensures the grass will crowd out any returning crabgrass.

Pulling Up Crabgrass

Another favorite natural method of killing crabgrass is labor intensive. Pull the weeds by hand, using a weeding tool, garden fork or a knife to dig around the clumps to loosen the soil.

Using Vinegar to Kill Crabgrass

You can also use distilled vinegar, full strength with a few drops of non-detergent dish washing soap poured into a gardening sprayer. The dish soap will assist the vinegar in sticking to the crabgrass You may want to try one of the horticultural vinegars, such as OSM Inc's Horticultural vinegar with yucca extract added to assist the vinegar in sticking to the crabgrass.

Saltwater Kills Crabgrass

You can mix household salt with water in a 1:1 ratio and use a garden sprayer to apply to crabgrass. Shake well to mix the solution. You can always heat the water to assist in quickly dissolving the salt. Completely saturate the unwanted clumps of crabgrass. The saltwater will soak into the ground and kill anything it contacts.

Cultivate Area of Dead Crabgrass

The most important step in killing crabgrass with any natural method is reseeding. Once the crabgrass has been killed, it's important to cultivate that area with grass seeds.

  1. Cover the dead crabgrass with compost.
  2. Add an overly generous amount of grass seed.
  3. Cover lightly with more compost.
  4. Water with slow flow to saturate the soil.
  5. Keep newly cultivated areas watered to encourage germination of grass seeds.
  6. Keep watering until the new grass patches are firmly established.
  7. Make sure you load the compost with grass seeds to ensure no space is available for new crabgrass to emerge.
  8. Repeat as needed in spring and fall to kill off crabgrass.
  9. This method may take a little longer to kill off the crabgrass, but it eliminates the need to use herbicides.

Plan of Action for Spring to Kill Crabgrass

You need a plan of action to kill crabgrass. Choose one of the many methods that best fits your gardening style and goals.

How to Kill Crabgrass